Boring and turning lathes



1966 J. N. COLEBROOK 3,232,139

BORING AND TURNING LATHES Original Filed July 5, 1961 4 Sheets-Sheet 1INVENTOR ATTORN EYS Nov. 1, 1966 J. N. COLEBROOK 3,282,139

BORING AND TURNING LATHES Original Filed July 5. 1961 4 Sheets-Sheet 2 Il i INVENTOR BY {id/KM ATTORNEYS Nov. 1, 1966 J. N. COLEBROOK 3,282,139

BORING AND TURNING LATHES Original Filed July 5. 1961 4 Sheets-Sheet 5INVENTOR M 4/. Al LJ ATTORN EYS Nov. 1, 1966 J. N. COLEBROQK BORING ANDTURNING LATHES 4 Sheets-Sheet 4 Original Filed July 5, 1961 INVENTQR M YWM ATTORNEYS III/ I I United States Patent 3,282,139 BURING AND TURNKNGLATI-HES James N. Colehrook, (Cincinnati, Uhio, assignor to The Lodge13; dhipley Company, Cincinnati, tlhio, a corporation of ()hio Uriginalapplication July 3, 1961, Ser. No. 123,361), new

Pat nt No. 3,186,269, dated lune 1, 1965. Divided and this applicationMar. 29, 1965, Ser. No. 443,191

3 Claims. (Cl. d22.5}

This application is a division of my copending application Serial No.123,360, filed July 3, 1961, now Patent 3,186,269 and entitledImprovements in Boring and Turning Lathes.

This invention relates to cutting type machine tools and in particularrelates to improvements in lathes constructed primarily for use inmachining parts as by turning and by contour boring.

In one aspect, the invention contemplates a lathe of the kind mentioned,havin a carriage which mounts independently operable turning and boringcross slides, respectively mounting turning and boring tool holders witheach slide and its holder being constructed and positionable so that oneslide with its holder and tool can function without interference fromthe other.

In another aspect, the invention contemplates a lathe oi the kindmentioned having a carriage which mounts physically separated andindependently operable-turning and boring cross slides respectivelymounting turning and boring tool holders, with the boring tool holderhaving means to swing a boring bar and tool to an operative position formachining a workpiece and to swing the bar and tool to inoperativeposition wherein the turning slide and its holder can be operatedwithout interference from the boring bar and tool.

In another aspect, the invention contemplates a lathe of the kindmentioned having a carriage which mounts inde endently operable turningand boring cross slides respectively mounting turning and boring toolholders with the turning cross slide and its holder being disposedbetween the boring cross slide and the lathe headstock, the boring toolholder having means mounting a boring bar and tool which in theoperative position extends into the path of motion of the turning crossslide and holder, but which is swingable to an inoperative position,wherein the bar and holder are free of the turning slide and holder sothat the same are operable without inter- -ference.

in another aspect, the invention contemplates a carriage which mountsindependently operable turning and boring cross slides respectivelymounting turning and boring tool holders, the turning cross slide andholder being disposed between the lathe headstock and the boring crossslide and the boring tool holder having means to mount a boring bar andtool so that the bar and tool can be quickly placed in an operativeposition or an inoperative position without moving the bar from theholder, the inoperative position permitting movement of the turningslide and holder without interference from the bar.

In another aspect, the invention contemplates for a lathe of the kind inquestion, a boring tool holder having a base adapted to be mounted on aslide and having a pair of spaced upright members between which ispivotedly mounted a support for holding a boring bar and tool, thesupport being swingable to a fixed horizontal position wherein the toolis conditioned for cutting and also swingable to a fixed verticalposition constituting a storage or non-use position.

In a still further aspect, the invention contemplates a lathe of thekind in question having a tracer controlled boring cross slide,improvements providing for the boring tool and tracer stylus to beindependently positionable Fatented Nov. 1, 1966 relative to each other,such positioning providing a simple and effective way (which especiallyuseful in narrow mouth boring jobs) to permit the boring tool after ithas finished the workpiece (and still inside the same) to be relievedand then brought out under rapid traverse without any danger of the toolor bar striking tl e neck of the part.

In another aspect, the invention contemplates in a lathe of the kind inquestion having a tracer controlled boring cross slide, improvements intracer means for controlling the operation of a boring tool to providefor the quick adjustment of relieved position of both tool and styluswhen replacing a template having a small minimum radius with a templatehaving a larger minimum radius.

In another aspect, the invention contemplates a lathe of the kind inquestion having an improved structure for the boring cross slide and itstracer controlled drive, the improved structure providing for the boringtool to be adjusted (along the slide motion axis) relative to the tracerstylus and to the tracer drive means, and also, provides for the stylusto be adjustable along the slide axis (independently of the firs-tadjustment) relative to the boring tool and the tracer drive means.

In another aspect, the invention contemplates a lathe of the kindmentioned having a carriage which mounts a boring cross slide includinga tracer slide and a boring tool slide which is positionable relative tothe tracer slide, the slides being movable in unison under tracercontrol and the tracer stylus being mounted on the tracer slide foradjustment relative to the slide.

A preferred embodiment of the invention will be described in connectionwith the following drawings, wherein:

FIGURE 1 is a plan view of a turning and contour boring latheconstructed in accordance with the invention;

FIGURE 2 is an elevational view of thelathe of FIG- URE 1;

FIGURE 3 is an elevational view of certain of the components of thelathe of FIGURES 1 and 2, particularly the carriage and the turning andboring cross slides;

FIGURE 4 is a sectional View taken along the lines 4--4 in FIGURE 3;

FIGURE 5 is an end view taken along the lines 55 in FIGURE 3;

FIGURES 6 and 7 are respectively diagrammatic sketches of a workpiece tobe machined and the control template for the same.

In FIGURE 1 the lathe includes a bed 1, a headstock 2, rotatablymounting a hollow workpiece WP which is to be turned and bored, and acarriage .3 mounted on ways 4 on the bed for reciprocating motion backand forth along the rotational axis of the workpiece. A boring crossslide, generally indicated by the numeral 5, and a turning cross slide 6are both mounted on the carriage for reciprocating motion in a directionat to the direction of the carriage movement.

The turning slide 6 mounts a holder 10 adapted to support a turning tool11, the 90 motion of the turning slide controlled by a conventional nutand screw arrangement manually operated by the wheel 12. The 90 motionof the turning slide provides for the tool 11 to be movable acrosscenter; i.e., across the rotational axis of the workpiece. In FIGURE 1the turning cross slide is positioned at its limit toward the front ofthe lathe.

The boring cross slide 5 mounts a holder 13 adapted to support a boringbar 14 carrying the boring tool 15. In FIGURES 1 and 2 the boring bar isin position for the tool to machine or cut material from the inside ofthe workpiece. This is the operative position of the boring bar. Bymeans which will be explained later, the boring 3 bar may be swung orpivoted into a vertical position as indicated by the dot-ted lines 14ain FIGURE 2.

The motion of the boring cross slide along the 90 axis is tracercontrolled, the fluid motor for the tracer being indicated at 16, thetracer valve at 17, the stylus at 1 3 which cooperates with a templatemounted on the bed. In FIGURE 1 the boring cross slide is in relievedposition or all the way to the rear of the lathe. When the cross slideis put in trace it moves toward the front of the machine or until thestylus 18 engages the template 20.

Without further detailed description, it will be seen that the abovestructure provides a carriage mounting turning and boring cross slideswhich are independently operable and respectively carry turning andboring tools. It is contemplated that the boring and turning operationsbe accomplished independently and not simultaneously as otherwise theturning tool might impose a variable load on the boring tool and causethe same to fail to follow the dictates of the tracer.

With reference to FIGURES l and 2, it will be observed that the turningcross slide and its holder are disposed between the headstock and theboring cross slide. The turning cross slide and its holder areconstructed so that when the machine is set up for a boring operation(as indicated in FIGURE 1) they are positioned toward the front of themachine, spaced from the boring bar and its holder and beyond the swingof the workpiece. In this position the boring'cross slide, holder andbar can be operated without interference from the turning elements.

During a turning operation, the boring tool, holder and cross slide areconditioned whereby the turning operation can be performed withoutinterference from the boring elements. Thus it will be apparent thatwith the boring bar in the position indicated at 14a it is spaced awayfrom the path of the turning tool holder. Further, it will be noted thatneither the boring cross slide nor the boring tool holder project intothe path of motion of the turning cross slide nor the turning toolholder.

Thus it is pointed out that the above described structure, comprisingboring and turning cross slides and holders commonly mounted on a singlecarriage and structurally arranged for independent operation withoutinterference from one another and particularly the swing up feature ofthe boring bar, constitute an important part of the invention. Theadvantages of this kind of construction will be readily apparent tothose skilled in the art. From the standpoint of high production thenoninterference feature is of particular significance because operationmay be changed from turning to boring or vice versa with a very minimumof effort on the part of the lathe operator. Additionally the abovedescribed structure represents an advance over conventional lathes(arranged primarily for turning and boring) from the standpoint of lowercosts, for example, dual carriages and multiplicity of controls for thesame have been eliminated and .it is unnecessary to use two independentlathes one for turning and one for boring.

With the above in mind then certain of the structural details of theabove mentioned components will be described below.

First of all the carriage 3 in itself is a generally flat H- shapedcasting, the H effect being provided by the cut-outs 22 and 23 (FIGURE1). With reference to FIGURE 4, it will be observed that the carriage isslidably mounted on the bed 1 by virtue of the ways 4. With reference toFIGURE 1, it will be noted that the center part of the H-shaped carriagestructin'e mounts the turning and boring cross slides. The front part ofthe carriage is connected with an apron 24 (FIGURE 2). The carriage isadapted to be reciprocated on the Ways by conventional drive mechanism,for example, the drive mechanism usually associated with an engine latheand for that reason the carriage drive or feed is not illustrated ordescribed.

The turning tool slide is a generally flat rectangular shaped memberwhich is mounted on the carriage for motion by means of the ways 25 and2e (FIGURE 3) which are fixedly secured to the carriage and guide theslides in the desired direction and over the appropriate distance. Aconventional nut and screw mechanism is adapted to move the carriage onthe 90 path, the screw being indicated at 30 in FIGURE 3. The screw isrotated by the wheel 12. Tie turning tool holder 10 is mounted on slide6 and extends generally upright therefrom. The holder 10 is somewhatrectangular in cross section and it is configured to contribute to thenon-interference condition commented on heretofore. The means 31 on theholder 10 for gripping tool 11 is conventional and need not further bedescribed.

The boring cross slide and its tracer drive have improvements which forman important part of the lathe. According to the invention the boringcross slide and its tracer drive are arranged to provide for moving theboring tool and tracer stylus in unison and also providing for relativeindependent positioning of the boring tool and stylus along the 90 axis.

For the above purpose, the boring cross slide comprises two componentslides, one a tracer slide which mounts the tracer valve and the other aboring tool slide which mounts the holder and boring bar. These slidesare interconnected to be movable in unison under the control of thetracer valve, but so that the boring tool slide can be adjusted alongthe 90 axis relative to the tracer slide without disturbing the stylusposition. The tracer stylus is mounted on the tracer slide by meansoperative so that the tracer valve can be adjusted along the 90 axisrelative to the tracer slide and hence to the boring tool slide orboring tool. Thus, as between the tracer stylus and the boring toolthere are two independent adjustments along the 90 axis. As will bepointed out more in detail hereinafter, the adjustment feature is mostadvantageous in a boring operation in that it permits the boring tool tobe relieved and brought out of the part at a rapid traverse without anypossible danger to the boring bar striking on the machine part. It willbe understood, of course, that this feature is of special significancefrom the standpoint of production because it permits the operator torapidly set up the machine for another operation after one has finished.Additionally, the adjusting feature is significantly advantageous whendifferent parts (requiring different templates) are to be bored, andparticularly, in cases where the new part has a larger minimum radiusthan the old part. In such instances, the adjusting feature permits theoperator to quickly set up the stylus and tool in the correct positionfor tracing.

The boring tool slide 34 and the tracer slide 35 (see FIGURES 1 and 4)are substantially flat rectangular castings and both mounted on commonways 37 secured to the carriage 3. The boring tool slide and the tracerslide are arranged to be moved in unison under the control of the tracerand for adjustment of the boring tool slide relative to the tracer slideby the mechanism which will be described following.

With reference to FIGURE 4, the tracer drive motor 16 comprises ahydraulic cylinder 40 which is fixed to the carriage 3. A piston 41 isdisposed within the cylinder for reciprocating motion, the motion of thepiston being along the 90 axis. Fluid for operating the piston iscontrolled by the tracer valve 17 in a well known manner and it isbelieved unnecessary for the benefit of those skilled in the art todescribe or illustrate a typical hydraulic tracer system. On the end ofthe piston 41, or more specifically, on the piston rod 42 there ismounted a hollow coupling member 43 which is connected by the thrustbearings 44 and 45 to a screw 46. The coupling 43 and bearings 44 and 45cause the screw 46 to be displaced along its axis with movement of thepiston, but

provide for the screw to be rotatable relative to the coupling andpiston.

The screw 46 is threaded as indicated and associated with the threads isa nut 50 which is a conventional twopart antibacl lash structure. Thenut Sit is fixed to the boring tool slide 34. Rotation of the nut causestranslation of the boring tool slide along the ways 37. The motion ofthe slide to the right (as viewed in FIGURE 4) is limited by theengagement of the nut with the stopcollar 51 and motion of the slide tothe left is limited by the stop-collar 52 pinned to the screw.Preferably the stroke of the slide is the same as the stroke of thepiston.

To the left of the stop-collar 52 the screw is not threaded and a set ofthrust bearings 53 and 54 rotatably couple the screw to a collar 55which is fixed to the tracer slide 35. This construction provides thatthe screw can be rotated relative to the tracer slide 35, but that withdisplacement of the screw along its axis the tracer slide 35 willpartake of the corresponding motion along its ways 37. The screw isadapted to be rotated by a wheel 56 which is supported by a bracket 60connected with the tracer slide.

In summary: Rotation of wheel 56 adjusts the boring tool slide 34relative to the tracer slide 36 and also relative to the tracer drive orpiston 41; when the screw 46 is moved by the piston 41, boring toolslide 34 and tracer slide 35 move in unison with the piston.

In the position of the parts as shown in FIGURE 4 (and also in FIGURES 1and 2), the boring cross slide is relieved; i.e., it is as far to therear of the machine as the travel of the piston 41 will permit. Also itwill be noted that the screw 46 has been rotated so that the boringslide 34 is at its maximum adjustment toward the rear of the machine.

The mounting of the tracer valve on the tracer slide 35 will next bedescribed.

With reference to FIGURES 4 and 5, it will be seen that the tracer slidehas an extension or bracket 61. The bracket 61 has a set of dovetails 62on which are dis posed a bottom slide 63. A wheel 64 is connected to aconventional nut and screw arrangement so that rotation of the wheelwill cause movement of the bottom slide 63. The dovetails 62 are set upso that the motion of the bottom slide 63 is parallel to the rotationalaxis of the workpiece. I

With reference to FIGURE 3, the bottom slide 63 carries a set ofdovetails 65 on which are disposed a top slide 4%. A wheel 7% isconnected to a conventional nut and screw arrangement so that rotationof the wheel causes the top slide as to move back and forth on thebottom slide. The dovetails d5 are set up so that this motion is alongthe 90 axis and the total stroke is preferably the same as the stroke ofpiston 41. The top slide 56 carries a supporting arm 71, which partakesof the motion of the top slide. The arm 71 mounts the tracer valve 17.

From the foregoing description, it will be apparent that with rotationof the wheel 70, the tracer stylus is adjusted along the 90 axis withrespect to the boring tool slide and hence with respect to the boringtool 15 supported by the slide (and also adjusted relative to the tracerdrive piston 41). The position of the boring tool is not disturbed bythis adjustment of the stylus. Also from the description of theadjustment of the boring to-ol slide (wheel 56) the boring tool can beadjusted along the 90 axis without disturbing the stylus adjustment.

The utilization of the adjustment of the tracer stylus, and theadjustment of the boring tool along the 90 axis will be commented onmore in detail hereinafter. First, however, it is desired to describethe structure of the boring tool holder 13.

With reference to FIGURES 3, 4 and 5 the boring tool holder 13 isgenerally U-shaped having a base or bridge member 81, which isconstructed to be secured to the boring tool slide 34 together with twovertically extending 6 legs 82 and 83. Across the mouth of the U, andconnected to the legs 32 and 83 is a stop member 84. Disposed betweenthe legs 82 and 83 is a support member 85 which is pivotally connectedwith the legs by the pivots 86 and 37. The support member carries theboring bar 14. As best shown in FIGURE 4, the stop member 84 has a pairof abutments 9% which are engaged with the support member 85. Theengagementbetween the abutments 9% and the support determines thelocation of the support to orient the boring bar and boring tool asshown in FIGURES l and 3; i.e., the operation or machining position. Thesupport member 85 has an aperture 91 which accepts the end of the boringbar 14 and the bar is clamped in position by means of the nuts 92 and93. The boring bar and support may be locked in the operative positionby means of the dog 94 which can be swung over the support by therotation of the handle 95.

The inoperative position of the support and boring bar is indicated bythe dot-dash lines 14a and 85a in FIGURE 3. It will be apparent that tomove the boring bar to the inoperative position it is simply necessaryto relieve the dog 94 and swing the bar upwardly about the pivots 86 and87. The boring bar and support can be locked in the up position by meansof the spring loaded plunger 93 which is adapted to fit into an aperture99 in the block when the same is in the inoperative position.

The boring bar holder as above described plays an important part in theoverall operation of the lathe particularly from the standpoint ofproviding a sound, firm structure which will adequately support andposition the boring bar and its connecting tool for a machiningoperation and especially in that the structure readily permits the barand tool to be quickly moved from the operative to the inoperativeposition and then back to the operative position without disturbing thedesired location of the tool for a boring operation. Furthermore, thestructure described functions and cooperates with the turning and boringcross slides and particularly with their configuration and structure anddisposition for interference free turning and bar machine work.

Returning now to the mounting arrangement described above for adjustablypositioning the boring tool and tracer stylus in the direction, thefollowing examples will sufiice to illustrate the advantages.

With reference to FIGURE 6, assume that a workpiece me has an internalcontoured surface 101 to be machined. The center line or rotational axisof the part is indicated atlltlZ. In FIGURE 7 template 103 forcontrolling the contour boring operation has a stylus engaging surfacelltlll' of the same shape as surface till and the template center linewhich corresponds to the part center line is indicated at W2. It will beobserved that the finished bore will have a minimum radius 105 which ismuch less than any other radius on the contour. (On the template radiusis indicated at 105'.) After a boring tool has machined the surface Tillof the workpiece (and is located, say, at the point 1%), it is highlydesirable that the tool be brought out of the work at the fastest ratepossible. If the boring slide is relieved there may be a likelihood ofthe boring bar or tool striking the mouth it)? of the piece. Theadjusting feature described heretofore provides for alleviating anypossibility of this condition.

Assuming that the borin cross slide is bottomed as shown in FIGURE 4,the wheel '70 is adjusted until the stylus 18 is slightly spaced fromthe minimum radius, for example, located at the point 168. The wheel 56then can be mani ulated to space the boring tool the same distance fromthe minimum radius 1.635 on the Workpiece as the stylus is from theminimum radius 105' or at point 1%. In such a position, of course, it isnecessary that the boring bar fully clear the mouth of the work. Sincethe foregoing rep-resents the relieved position of the boring crossslide it will be apparent that after the surface Kill has been machinedor when the tool has reached the point indicated by 106 relieving thecross slide will simply cause the tool to move radially to a position10? which corresponds to point 108. Thus the boring bar will free fromthe mouth. At this time the carriage can be moved to the rear at rapidtraverse and the tool brought out of the piece without any danger ofeither the bar or the tool colliding with a workpiece.

Actually, of course, when the stylus and tool are initially adjusted tothe points 108 and 108', the handle 56 may be manipulated to bring inthe tool closer to the piece for skimming or rough cuts and for finaladjustment for the finish cut.

For maximum advantage to be taken of the adjusting feature it iscontemplated that any template used in the machine be of a type suchthat the maximum radius of the contour is always located at a fixeddistance from a datum surface on the template. For example, in FIG- URE7 the template m3 has a datum surface 110 and a maximum radiusasindicated at lill. This maximum radius is always located at a fixeddistance 112 from the datum surface 116. Any other template which is tobe substituted in the machine should be set up in the similar manner,that is that the maximum radius be located a fixed distance from thedatum surface. Referring to FIGURE 4, the lathe is also provided with afixed datum surface 113 to locate the template datum surface 110. Thedatum surface 113 is formed on block 114 fixed to the bed. The templateis held on the block by the dogs 116. The datum surface 113 is at afixed and known position from the vertical plane containing therotational axis of the work.

A type of template mentioned above and the 90 stylus adjustment (bywheel 7%) and the 90 boring tool adjustment (by wheel 56) cooperate toprovide for quick adjustment of relieved position of tool and styluswhen changing the templates.

With reference to FIGURE 6 assumes a new part having a larger minimumradius, for example, as indicated at- 115 were to be bored. This wouldrequire a new template having a minimum radius as indicated at 115'.With the stylus and the tool in the relieved position of the previousjob (near points 168' and 108) starting tracer operation would requiremovement from the relieved position to the new minimum radius position.This movement would be relatively slow and considerable time would belost in repeat operations on the same part. By simply adjusting thewheels 56 and 70, the tool and stylus can be brought into the desiredposition with respect to the new minimum radius.

In connection with the internal configuration of the workpiece of FIGURE6, it will be appreciated that the particular contour shown is fordescriptive purposes.

I claim: 1. In a machine tool: a carriage mounted for reciprocatingmotion along an axis;

means mounting a turning tool cross slide and a boring tool cross slideadjacent to one another on said carriage for independent reciprocatingmotion on the carriage along spaced apart, parallel axes extendingnormal to said carriage motion axis;

:a generally U-shaped member, the bridge of the U being mounted on saidboring tool cross slide with the legs of the U extending generallyvertically;

support means disposed between said legs, the support having means formounting a boring bar;

pivot connections between said support and said legs providing for thesupport to be rotatable about a horizontal axis to an operativeposition-wherein a boring bar in the holder will extend generallyhorizontally across the path of motion of the turning tool slide and toan inoperative position wherein a boring bar will extend generallyvertically and away from the path of motion of the turning tool slide;and

a stop member connected to and extending between the mouth of said legs,the stop member being positioned to be engaged by said support uponrotation thereof to the operative position.

2. In a machine tool:

a carriage mounted for reciprocating motion along an axis;

means mounting a turning tool cross slide and a boring tool cross slideside by side on the carriage for independent reciprocating motion on thecarriage along generally spaced apart, axes extending normal to saidcarriage motion axis;

a turning holder on the turning tool cross slide;

a member mounted on the boring tool cross slide in a manner to extendupright therefrom;

a boring tool support having means for mounting a boring bar;

pivot connections between said boring tool support and said. memberproviding for the support to be rotatable to an operative positionwherein a boring bar mounted in the support extends into the path ofmotion of the turning tool holder and the pivot connection alsoproviding for the support to be rotatable to an inoperative positionwherein a boring bar mounted in the holder is free from said path;

stop means mounted on said member to be engaged by said support todetermine said operative position; and

mechanism mounted on said member and movable when said support hasengaged said stop means to engage the support and lock the same firmagainst the stop means.

3. In a machine tool:

a carriage mounted for reciprocating motion along an axis;

means mounting a turning tool cross slide and a boring tool cross slideadjacent to one another on said carriage for independent reciprocatingmotion on the carriage along spaced apart, parallel axes extendingnormal to said carriage motion axis;

a generally U-shaped member, the bridge of the U being mounted on saidboring tool cross slide with the legs of the U extending generallyvertically;

support means disposed between said legs, the support having means formounting a boring bar;

pivot connections between said support and said legs providing for thesupport to be rotatable about a horizontal axis to an operative positionwherein a boring bar in the holder will extend generally horizontallyacross the path of motion of the turning tool slide and to aninoperative position wherein a boring bar will extend generallyvertically and away from the path of motion of the turning tool slide;

a stop member connected to and extending between the mouth of said legs,the stop member being positioned to be engaged by said support uponrotation thereof to the operative position; and

means on one of said legs and movable when-the support has engaged thestop member to engage the support and lock the same firm against thestop means.

References Cited by the Examiner UNITED STATES PATENTS 922,082 5/1909Buckius 29 27 x 2,316,405 4/1943 Clausen 29-27 X 2,627,194 2/1953 Leiferet a1. 29 27 FOREIGN PATENTS 77,415 4/1918 Switzerland.

WILLIAM W. DYER, In, Primary Examiner.

G. A. DOST, Assistant Examiner.

1. IN A MACHINE TOOL: A CARRIAGE MOUNTED FOR RECIPROCATING MOTION ALONGAN AXIS; MEANS MOUNTING A TURNING TOOL CROSS SLIDE AND A BORING TOOLCROSS SLIDE ADJACENT TO ONE ANOTHER ON SAID CARRIAGE FOR INDEPENDENTRECIPROCATING MOTION ON THE CARRIAGE ALONG SPACED APART, PARALLEL AXESEXTENDING NORMAL TO SAID CARRIAGE MOTION AXIS; A GENERALLY U-SHAPEDMEMBER, THE BRIDGE OF THE U BEING MOUNTED ON SAID BORING TOOL CROSSSLIDE WITH THE LEGS OF THE U EXTENDING GENERALLY VERTICALLY; SUPPORTMEANS DISPOSED BETWEEN SAID LEGS, THE SUPPORT HAVING MEANS FOR MOUNTINGA BORING BAR; PIVOT CONNECTIONS BETWEEN SAID SUPPORT AND SAID LEGSPROVIDING FOR THE SUPPORT TO BE ROTATABLE ABOUT A HORIZONTAL AXIS TO ANOPERATIVE POSITION WHEREIN A BORING BAR IN THE HOLDER WILL EXTENDGENERALLY HORIZONTALLY ACROSS THE PATH OF MOTION OF THE TURNING TOOLSLIDE TO AN INOPERATIVE POSITION WHEREIN A BORING BAR WILL EXTENDGENERALLY VERTICALLY AND AWAY FROM THE PATH OF MOTION OF THE TURNINGTOOL SLIDE; AND A STOP MEMBER CONNECTED TO AND EXTENDING BETWEEN THEMOUTH OF SAID LEGS, THE STOP MEMBER BEING POSITIONED TO BE ENGAGED BYSAID SUPPORT UPON ROTATION THEREOF TO THE OPERATIVE POSITION.